RdrHsSyn.hs

--
--  (c) The University of Glasgow 2002-2006
--

-- Functions over HsSyn specialised to RdrName.

{-# LANGUAGE CPP #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE MagicHash #-}
{-# LANGUAGE ViewPatterns #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}

module   RdrHsSyn (
        mkHsOpApp,
        mkHsIntegral, mkHsFractional, mkHsIsString,
        mkHsDo, mkSpliceDecl,
        mkRoleAnnotDecl,
        mkClassDecl,
        mkTyData, mkDataFamInst,
        mkTySynonym, mkTyFamInstEqn,
        mkStandaloneKindSig,
        mkTyFamInst,
        mkFamDecl, mkLHsSigType,
        mkInlinePragma,
        mkPatSynMatchGroup,
        mkRecConstrOrUpdate, -- HsExp -> [HsFieldUpdate] -> P HsExp
        mkTyClD, mkInstD,
        mkRdrRecordCon, mkRdrRecordUpd,
        setRdrNameSpace,
        filterCTuple,

        cvBindGroup,
        cvBindsAndSigs,
        cvTopDecls,
        placeHolderPunRhs,

        -- Stuff to do with Foreign declarations
        mkImport,
        parseCImport,
        mkExport,
        mkExtName,    -- RdrName -> CLabelString
        mkGadtDecl,   -- [Located RdrName] -> LHsType RdrName -> ConDecl RdrName
        mkConDeclH98,

        -- Bunch of functions in the parser monad for
        -- checking and constructing values
        checkImportDecl,
        checkExpBlockArguments,
        checkPrecP,           -- Int -> P Int
        checkContext,         -- HsType -> P HsContext
        checkPattern,         -- HsExp -> P HsPat
        checkPattern_msg,
        checkMonadComp,       -- P (HsStmtContext GhcPs)
        checkValDef,          -- (SrcLoc, HsExp, HsRhs, [HsDecl]) -> P HsDecl
        checkValSigLhs,
        LRuleTyTmVar, RuleTyTmVar(..),
        mkRuleBndrs, mkRuleTyVarBndrs,
        checkRuleTyVarBndrNames,
        checkRecordSyntax,
        checkEmptyGADTs,
        addFatalError, hintBangPat,
        TyEl(..), mergeOps, mergeDataCon,
        mkBangTy,

        -- Help with processing exports
        ImpExpSubSpec(..),
        ImpExpQcSpec(..),
        mkModuleImpExp,
        mkTypeImpExp,
        mkImpExpSubSpec,
        checkImportSpec,

        -- Token symbols
        forallSym,
        starSym,

        -- Warnings and errors
        warnStarIsType,
        warnPrepositiveQualifiedModule,
        failOpFewArgs,
        failOpNotEnabledImportQualifiedPost,
        failOpImportQualifiedTwice,

        SumOrTuple (..),

        -- Expression/command/pattern ambiguity resolution
        PV,
        runPV,
        ECP(ECP, runECP_PV),
        runECP_P,
        DisambInfixOp(..),
        DisambECP(..),
        ecpFromExp,
        ecpFromCmd,
        PatBuilder,

    ) where

import GhcPrelude
import GHC.Hs           -- Lots of it
import TyCon            ( TyCon, isTupleTyCon, tyConSingleDataCon_maybe )
import DataCon          ( DataCon, dataConTyCon )
import ConLike          ( ConLike(..) )
import CoAxiom          ( Role, fsFromRole )
import RdrName
import Name
import BasicTypes
import Lexer
import Lexeme           ( isLexCon )
import Type             ( TyThing(..), funTyCon )
import TysWiredIn       ( cTupleTyConName, tupleTyCon, tupleDataCon,
                          nilDataConName, nilDataConKey,
                          listTyConName, listTyConKey, eqTyCon_RDR,
                          tupleTyConName, cTupleTyConNameArity_maybe )
import ForeignCall
import PrelNames        ( allNameStrings )
import SrcLoc
import Unique           ( hasKey )
import OrdList          ( OrdList, fromOL )
import Bag              ( emptyBag, consBag )
import Outputable
import FastString
import Maybes
import Util
import ApiAnnotation
import Data.List
import DynFlags ( WarningFlag(..), DynFlags )
import ErrUtils ( Messages )

import Control.Monad
import Text.ParserCombinators.ReadP as ReadP
import Data.Char
import qualified Data.Monoid as Monoid
import Data.Data       ( dataTypeOf, fromConstr, dataTypeConstrs )
import Data.Kind       ( Type )

#include "HsVersions.h"


{- **********************************************************************

  Construction functions for Rdr stuff

  ********************************************************************* -}

-- | mkClassDecl builds a RdrClassDecl, filling in the names for tycon and
-- datacon by deriving them from the name of the class.  We fill in the names
-- for the tycon and datacon corresponding to the class, by deriving them
-- from the name of the class itself.  This saves recording the names in the
-- interface file (which would be equally good).

-- Similarly for mkConDecl, mkClassOpSig and default-method names.

--         *** See Note [The Naming story] in GHC.Hs.Decls ****

mkTyClD :: LTyClDecl (GhcPass p) -> LHsDecl (GhcPass p)
mkTyClD (L loc d) = L loc (TyClD noExtField d)

mkInstD :: LInstDecl (GhcPass p) -> LHsDecl (GhcPass p)
mkInstD (L loc d) = L loc (InstD noExtField d)

mkClassDecl :: SrcSpan
            -> Located (Maybe (LHsContext GhcPs), LHsType GhcPs)
            -> Located (a,[LHsFunDep GhcPs])
            -> OrdList (LHsDecl GhcPs)
            -> P (LTyClDecl GhcPs)

mkClassDecl loc (L _ (mcxt, tycl_hdr)) fds where_cls
  = do { (binds, sigs, ats, at_defs, _, docs) <- cvBindsAndSigs where_cls
       ; let cxt = fromMaybe (noLoc []) mcxt
       ; (cls, tparams, fixity, ann) <- checkTyClHdr True tycl_hdr
       ; addAnnsAt loc ann -- Add any API Annotations to the top SrcSpan
       ; (tyvars,annst) <- checkTyVars (text "class") whereDots cls tparams
       ; addAnnsAt loc annst -- Add any API Annotations to the top SrcSpan
       ; return (L loc (ClassDecl { tcdCExt = noExtField, tcdCtxt = cxt
                                  , tcdLName = cls, tcdTyVars = tyvars
                                  , tcdFixity = fixity
                                  , tcdFDs = snd (unLoc fds)
                                  , tcdSigs = mkClassOpSigs sigs
                                  , tcdMeths = binds
                                  , tcdATs = ats, tcdATDefs = at_defs
                                  , tcdDocs  = docs })) }

mkTyData :: SrcSpan
         -> NewOrData
         -> Maybe (Located CType)
         -> Located (Maybe (LHsContext GhcPs), LHsType GhcPs)
         -> Maybe (LHsKind GhcPs)
         -> [LConDecl GhcPs]
         -> HsDeriving GhcPs
         -> P (LTyClDecl GhcPs)
mkTyData loc new_or_data cType (L _ (mcxt, tycl_hdr))
         ksig data_cons maybe_deriv
  = do { (tc, tparams, fixity, ann) <- checkTyClHdr False tycl_hdr
       ; addAnnsAt loc ann -- Add any API Annotations to the top SrcSpan
       ; (tyvars, anns) <- checkTyVars (ppr new_or_data) equalsDots tc tparams
       ; addAnnsAt loc anns -- Add any API Annotations to the top SrcSpan
       ; defn <- mkDataDefn new_or_data cType mcxt ksig data_cons maybe_deriv
       ; return (L loc (DataDecl { tcdDExt = noExtField,
                                   tcdLName = tc, tcdTyVars = tyvars,
                                   tcdFixity = fixity,
                                   tcdDataDefn = defn })) }

mkDataDefn :: NewOrData
           -> Maybe (Located CType)
           -> Maybe (LHsContext GhcPs)
           -> Maybe (LHsKind GhcPs)
           -> [LConDecl GhcPs]
           -> HsDeriving GhcPs
           -> P (HsDataDefn GhcPs)
mkDataDefn new_or_data cType mcxt ksig data_cons maybe_deriv
  = do { checkDatatypeContext mcxt
       ; let cxt = fromMaybe (noLoc []) mcxt
       ; return (HsDataDefn { dd_ext = noExtField
                            , dd_ND = new_or_data, dd_cType = cType
                            , dd_ctxt = cxt
                            , dd_cons = data_cons
                            , dd_kindSig = ksig
                            , dd_derivs = maybe_deriv }) }


mkTySynonym :: SrcSpan
            -> LHsType GhcPs  -- LHS
            -> LHsType GhcPs  -- RHS
            -> P (LTyClDecl GhcPs)
mkTySynonym loc lhs rhs
  = do { (tc, tparams, fixity, ann) <- checkTyClHdr False lhs
       ; addAnnsAt loc ann -- Add any API Annotations to the top SrcSpan
       ; (tyvars, anns) <- checkTyVars (text "type") equalsDots tc tparams
       ; addAnnsAt loc anns -- Add any API Annotations to the top SrcSpan
       ; return (L loc (SynDecl { tcdSExt = noExtField
                                , tcdLName = tc, tcdTyVars = tyvars
                                , tcdFixity = fixity
                                , tcdRhs = rhs })) }

mkStandaloneKindSig
  :: SrcSpan
  -> Located [Located RdrName] -- LHS
  -> LHsKind GhcPs             -- RHS
  -> P (LStandaloneKindSig GhcPs)
mkStandaloneKindSig loc lhs rhs =
  do { vs <- mapM check_lhs_name (unLoc lhs)
     ; v <- check_singular_lhs (reverse vs)
     ; return $ L loc $ StandaloneKindSig noExtField v (mkLHsSigType rhs) }
  where
    check_lhs_name v@(unLoc->name) =
      if isUnqual name && isTcOcc (rdrNameOcc name)
      then return v
      else addFatalError (getLoc v) $
           hang (text "Expected an unqualified type constructor:") 2 (ppr v)
    check_singular_lhs vs =
      case vs of
        [] -> panic "mkStandaloneKindSig: empty left-hand side"
        [v] -> return v
        _ -> addFatalError (getLoc lhs) $
             vcat [ hang (text "Standalone kind signatures do not support multiple names at the moment:")
                       2 (pprWithCommas ppr vs)
                  , text "See https://gitlab.haskell.org/ghc/ghc/issues/16754 for details." ]

mkTyFamInstEqn :: Maybe [LHsTyVarBndr GhcPs]
               -> LHsType GhcPs
               -> LHsType GhcPs
               -> P (TyFamInstEqn GhcPs,[AddAnn])
mkTyFamInstEqn bndrs lhs rhs
  = do { (tc, tparams, fixity, ann) <- checkTyClHdr False lhs
       ; return (mkHsImplicitBndrs
                  (FamEqn { feqn_ext    = noExtField
                          , feqn_tycon  = tc
                          , feqn_bndrs  = bndrs
                          , feqn_pats   = tparams
                          , feqn_fixity = fixity
                          , feqn_rhs    = rhs }),
                 ann) }

mkDataFamInst :: SrcSpan
              -> NewOrData
              -> Maybe (Located CType)
              -> (Maybe ( LHsContext GhcPs), Maybe [LHsTyVarBndr GhcPs]
                        , LHsType GhcPs)
              -> Maybe (LHsKind GhcPs)
              -> [LConDecl GhcPs]
              -> HsDeriving GhcPs
              -> P (LInstDecl GhcPs)
mkDataFamInst loc new_or_data cType (mcxt, bndrs, tycl_hdr)
              ksig data_cons maybe_deriv
  = do { (tc, tparams, fixity, ann) <- checkTyClHdr False tycl_hdr
       ; addAnnsAt loc ann -- Add any API Annotations to the top SrcSpan
       ; defn <- mkDataDefn new_or_data cType mcxt ksig data_cons maybe_deriv
       ; return (L loc (DataFamInstD noExtField (DataFamInstDecl (mkHsImplicitBndrs
                  (FamEqn { feqn_ext    = noExtField
                          , feqn_tycon  = tc
                          , feqn_bndrs  = bndrs
                          , feqn_pats   = tparams
                          , feqn_fixity = fixity
                          , feqn_rhs    = defn }))))) }

mkTyFamInst :: SrcSpan
            -> TyFamInstEqn GhcPs
            -> P (LInstDecl GhcPs)
mkTyFamInst loc eqn
  = return (L loc (TyFamInstD noExtField (TyFamInstDecl eqn)))

mkFamDecl :: SrcSpan
          -> FamilyInfo GhcPs
          -> LHsType GhcPs                   -- LHS
          -> Located (FamilyResultSig GhcPs) -- Optional result signature
          -> Maybe (LInjectivityAnn GhcPs)   -- Injectivity annotation
          -> P (LTyClDecl GhcPs)
mkFamDecl loc info lhs ksig injAnn
  = do { (tc, tparams, fixity, ann) <- checkTyClHdr False lhs
       ; addAnnsAt loc ann -- Add any API Annotations to the top SrcSpan
       ; (tyvars, anns) <- checkTyVars (ppr info) equals_or_where tc tparams
       ; addAnnsAt loc anns -- Add any API Annotations to the top SrcSpan
       ; return (L loc (FamDecl noExtField (FamilyDecl
                                           { fdExt       = noExtField
                                           , fdInfo      = info, fdLName = tc
                                           , fdTyVars    = tyvars
                                           , fdFixity    = fixity
                                           , fdResultSig = ksig
                                           , fdInjectivityAnn = injAnn }))) }
  where
    equals_or_where = case info of
                        DataFamily          -> empty
                        OpenTypeFamily      -> empty
                        ClosedTypeFamily {} -> whereDots

mkSpliceDecl :: LHsExpr GhcPs -> HsDecl GhcPs
-- If the user wrote
--      [pads| ... ]   then return a QuasiQuoteD
--      $(e)           then return a SpliceD
-- but if she wrote, say,
--      f x            then behave as if she'd written $(f x)
--                     ie a SpliceD
--
-- Typed splices are not allowed at the top level, thus we do not represent them
-- as spliced declaration.  See #10945
mkSpliceDecl lexpr@(L loc expr)
  | HsSpliceE _ splice@(HsUntypedSplice {}) <- expr
  = SpliceD noExtField (SpliceDecl noExtField (L loc splice) ExplicitSplice)

  | HsSpliceE _ splice@(HsQuasiQuote {}) <- expr
  = SpliceD noExtField (SpliceDecl noExtField (L loc splice) ExplicitSplice)

  | otherwise
  = SpliceD noExtField (SpliceDecl noExtField (L loc (mkUntypedSplice BareSplice lexpr))
                              ImplicitSplice)

mkRoleAnnotDecl :: SrcSpan
                -> Located RdrName                -- type being annotated
                -> [Located (Maybe FastString)]      -- roles
                -> P (LRoleAnnotDecl GhcPs)
mkRoleAnnotDecl loc tycon roles
  = do { roles' <- mapM parse_role roles
       ; return $ L loc $ RoleAnnotDecl noExtField tycon roles' }
  where
    role_data_type = dataTypeOf (undefined :: Role)
    all_roles = map fromConstr $ dataTypeConstrs role_data_type
    possible_roles = [(fsFromRole role, role) | role <- all_roles]

    parse_role (L loc_role Nothing) = return $ L loc_role Nothing
    parse_role (L loc_role (Just role))
      = case lookup role possible_roles of
          Just found_role -> return $ L loc_role $ Just found_role
          Nothing         ->
            let nearby = fuzzyLookup (unpackFS role)
                  (mapFst unpackFS possible_roles)
            in
            addFatalError loc_role
              (text "Illegal role name" <+> quotes (ppr role) $$
               suggestions nearby)

    suggestions []   = empty
    suggestions [r]  = text "Perhaps you meant" <+> quotes (ppr r)
      -- will this last case ever happen??
    suggestions list = hang (text "Perhaps you meant one of these:")
                       2 (pprWithCommas (quotes . ppr) list)

{- **********************************************************************

  #cvBinds-etc# Converting to @HsBinds@, etc.

  ********************************************************************* -}

-- | Function definitions are restructured here. Each is assumed to be recursive
-- initially, and non recursive definitions are discovered by the dependency
-- analyser.


--  | Groups together bindings for a single function
cvTopDecls :: OrdList (LHsDecl GhcPs) -> [LHsDecl GhcPs]
cvTopDecls decls = go (fromOL decls)
  where
    go :: [LHsDecl GhcPs] -> [LHsDecl GhcPs]
    go []                     = []
    go ((L l (ValD x b)) : ds)
      = L l' (ValD x b') : go ds'
        where (L l' b', ds') = getMonoBind (L l b) ds
    go (d : ds)                    = d : go ds

-- Declaration list may only contain value bindings and signatures.
cvBindGroup :: OrdList (LHsDecl GhcPs) -> P (HsValBinds GhcPs)
cvBindGroup binding
  = do { (mbs, sigs, fam_ds, tfam_insts
         , dfam_insts, _) <- cvBindsAndSigs binding
       ; ASSERT( null fam_ds && null tfam_insts && null dfam_insts)
         return $ ValBinds noExtField mbs sigs }

cvBindsAndSigs :: OrdList (LHsDecl GhcPs)
  -> P (LHsBinds GhcPs, [LSig GhcPs], [LFamilyDecl GhcPs]
          , [LTyFamInstDecl GhcPs], [LDataFamInstDecl GhcPs], [LDocDecl])
-- Input decls contain just value bindings and signatures
-- and in case of class or instance declarations also
-- associated type declarations. They might also contain Haddock comments.
cvBindsAndSigs fb = go (fromOL fb)
  where
    go []              = return (emptyBag, [], [], [], [], [])
    go ((L l (ValD _ b)) : ds)
      = do { (bs, ss, ts, tfis, dfis, docs) <- go ds'
           ; return (b' `consBag` bs, ss, ts, tfis, dfis, docs) }
      where
        (b', ds') = getMonoBind (L l b) ds
    go ((L l decl) : ds)
      = do { (bs, ss, ts, tfis, dfis, docs) <- go ds
           ; case decl of
               SigD _ s
                 -> return (bs, L l s : ss, ts, tfis, dfis, docs)
               TyClD _ (FamDecl _ t)
                 -> return (bs, ss, L l t : ts, tfis, dfis, docs)
               InstD _ (TyFamInstD { tfid_inst = tfi })
                 -> return (bs, ss, ts, L l tfi : tfis, dfis, docs)
               InstD _ (DataFamInstD { dfid_inst = dfi })
                 -> return (bs, ss, ts, tfis, L l dfi : dfis, docs)
               DocD _ d
                 -> return (bs, ss, ts, tfis, dfis, L l d : docs)
               SpliceD _ d
                 -> addFatalError l $
                    hang (text "Declaration splices are allowed only" <+>
                          text "at the top level:")
                       2 (ppr d)
               _ -> pprPanic "cvBindsAndSigs" (ppr decl) }

-----------------------------------------------------------------------------
-- Group function bindings into equation groups

getMonoBind :: LHsBind GhcPs -> [LHsDecl GhcPs]
  -> (LHsBind GhcPs, [LHsDecl GhcPs])
-- Suppose      (b',ds') = getMonoBind b ds
--      ds is a list of parsed bindings
--      b is a MonoBinds that has just been read off the front

-- Then b' is the result of grouping more equations from ds that
-- belong with b into a single MonoBinds, and ds' is the depleted
-- list of parsed bindings.
--
-- All Haddock comments between equations inside the group are
-- discarded.
--
-- No AndMonoBinds or EmptyMonoBinds here; just single equations

getMonoBind (L loc1 (FunBind { fun_id = fun_id1@(L _ f1)
                             , fun_matches =
                               MG { mg_alts = (L _ mtchs1) } }))
            binds
  | has_args mtchs1
  = go mtchs1 loc1 binds []
  where
    go mtchs loc
       ((L loc2 (ValD _ (FunBind { fun_id = (L _ f2)
                                 , fun_matches =
                                    MG { mg_alts = (L _ mtchs2) } })))
         : binds) _
        | f1 == f2 = go (mtchs2 ++ mtchs)
                        (combineSrcSpans loc loc2) binds []
    go mtchs loc (doc_decl@(L loc2 (DocD {})) : binds) doc_decls
        = let doc_decls' = doc_decl : doc_decls
          in go mtchs (combineSrcSpans loc loc2) binds doc_decls'
    go mtchs loc binds doc_decls
        = ( L loc (makeFunBind fun_id1 (reverse mtchs))
          , (reverse doc_decls) ++ binds)
        -- Reverse the final matches, to get it back in the right order
        -- Do the same thing with the trailing doc comments

getMonoBind bind binds = (bind, binds)

has_args :: [LMatch GhcPs (LHsExpr GhcPs)] -> Bool
has_args []                                  = panic "RdrHsSyn:has_args"
has_args (L _ (Match { m_pats = args }) : _) = not (null args)
        -- Don't group together FunBinds if they have
        -- no arguments.  This is necessary now that variable bindings
        -- with no arguments are now treated as FunBinds rather
        -- than pattern bindings (tests/rename/should_fail/rnfail002).
has_args (L _ (XMatch nec) : _) = noExtCon nec

{- **********************************************************************

  #PrefixToHS-utils# Utilities for conversion

  ********************************************************************* -}

{- Note [Parsing data constructors is hard]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The problem with parsing data constructors is that they look a lot like types.
Compare:

  (s1)   data T = C t1 t2
  (s2)   type T = C t1 t2

Syntactically, there's little difference between these declarations, except in
(s1) 'C' is a data constructor, but in (s2) 'C' is a type constructor.

This similarity would pose no problem if we knew ahead of time if we are
parsing a type or a constructor declaration. Looking at (s1) and (s2), a simple
(but wrong!) rule comes to mind: in 'data' declarations assume we are parsing
data constructors, and in other contexts (e.g. 'type' declarations) assume we
are parsing type constructors.

This simple rule does not work because of two problematic cases:

  (p1)   data T = C t1 t2 :+ t3
  (p2)   data T = C t1 t2 => t3

In (p1) we encounter (:+) and it turns out we are parsing an infix data
declaration, so (C t1 t2) is a type and 'C' is a type constructor.
In (p2) we encounter (=>) and it turns out we are parsing an existential
context, so (C t1 t2) is a constraint and 'C' is a type constructor.

As the result, in order to determine whether (C t1 t2) declares a data
constructor, a type, or a context, we would need unlimited lookahead which
'happy' is not so happy with.

To further complicate matters, the interpretation of (!) and (~) is different
in constructors and types:

  (b1)   type T = C ! D
  (b2)   data T = C ! D
  (b3)   data T = C ! D => E

In (b1) and (b3), (!) is a type operator with two arguments: 'C' and 'D'. At
the same time, in (b2) it is a strictness annotation: 'C' is a data constructor
with a single strict argument 'D'. For the programmer, these cases are usually
easy to tell apart due to whitespace conventions:

  (b2)   data T = C !D         -- no space after the bang hints that
                               -- it is a strictness annotation

For the parser, on the other hand, this whitespace does not matter. We cannot
tell apart (b2) from (b3) until we encounter (=>), so it requires unlimited
lookahead.

The solution that accounts for all of these issues is to initially parse data
declarations and types as a reversed list of TyEl:

  data TyEl = TyElOpr RdrName
            | TyElOpd (HsType GhcPs)
            | ...

For example, both occurrences of (C ! D) in the following example are parsed
into equal lists of TyEl:

  data T = C ! D => C ! D   results in   [ TyElOpd (HsTyVar "D")
                                         , TyElOpr "!"
                                         , TyElOpd (HsTyVar "C") ]

Note that elements are in reverse order. Also, 'C' is parsed as a type
constructor (HsTyVar) even when it is a data constructor. We fix this in
`tyConToDataCon`.

By the time the list of TyEl is assembled, we have looked ahead enough to
decide whether to reduce using `mergeOps` (for types) or `mergeDataCon` (for
data constructors). These functions are where the actual job of parsing is
done.

-}

-- | Reinterpret a type constructor, including type operators, as a data
--   constructor.
-- See Note [Parsing data constructors is hard]
tyConToDataCon :: SrcSpan -> RdrName -> Either (SrcSpan, SDoc) (Located RdrName)
tyConToDataCon loc tc
  | isTcOcc occ || isDataOcc occ
  , isLexCon (occNameFS occ)
  = return (L loc (setRdrNameSpace tc srcDataName))

  | otherwise
  = Left (loc, msg)
  where
    occ = rdrNameOcc tc
    msg = text "Not a data constructor:" <+> quotes (ppr tc)

mkPatSynMatchGroup :: Located RdrName
                   -> Located (OrdList (LHsDecl GhcPs))
                   -> P (MatchGroup GhcPs (LHsExpr GhcPs))
mkPatSynMatchGroup (L loc patsyn_name) (L _ decls) =
    do { matches <- mapM fromDecl (fromOL decls)
       ; when (null matches) (wrongNumberErr loc)
       ; return $ mkMatchGroup FromSource matches }
  where
    fromDecl (L loc decl@(ValD _ (PatBind _
                         pat@(L _ (ConPatIn ln@(L _ name) details))
                               rhs _))) =
        do { unless (name == patsyn_name) $
               wrongNameBindingErr loc decl
           ; match <- case details of
               PrefixCon pats -> return $ Match { m_ext = noExtField
                                                , m_ctxt = ctxt, m_pats = pats
                                                , m_grhss = rhs }
                   where
                     ctxt = FunRhs { mc_fun = ln
                                   , mc_fixity = Prefix
                                   , mc_strictness = NoSrcStrict }

               InfixCon p1 p2 -> return $ Match { m_ext = noExtField
                                                , m_ctxt = ctxt
                                                , m_pats = [p1, p2]
                                                , m_grhss = rhs }
                   where
                     ctxt = FunRhs { mc_fun = ln
                                   , mc_fixity = Infix
                                   , mc_strictness = NoSrcStrict }

               RecCon{} -> recordPatSynErr loc pat
           ; return $ L loc match }
    fromDecl (L loc decl) = extraDeclErr loc decl

    extraDeclErr loc decl =
        addFatalError loc $
        text "pattern synonym 'where' clause must contain a single binding:" $$
        ppr decl

    wrongNameBindingErr loc decl =
      addFatalError loc $
      text "pattern synonym 'where' clause must bind the pattern synonym's name"
      <+> quotes (ppr patsyn_name) $$ ppr decl

    wrongNumberErr loc =
      addFatalError loc $
      text "pattern synonym 'where' clause cannot be empty" $$
      text "In the pattern synonym declaration for: " <+> ppr (patsyn_name)

recordPatSynErr :: SrcSpan -> LPat GhcPs -> P a
recordPatSynErr loc pat =
    addFatalError loc $
    text "record syntax not supported for pattern synonym declarations:" $$
    ppr pat

mkConDeclH98 :: Located RdrName -> Maybe [LHsTyVarBndr GhcPs]
                -> Maybe (LHsContext GhcPs) -> HsConDeclDetails GhcPs
                -> ConDecl GhcPs

mkConDeclH98 name mb_forall mb_cxt args
  = ConDeclH98 { con_ext    = noExtField
               , con_name   = name
               , con_forall = noLoc $ isJust mb_forall
               , con_ex_tvs = mb_forall `orElse` []
               , con_mb_cxt = mb_cxt
               , con_args   = args
               , con_doc    = Nothing }

mkGadtDecl :: [Located RdrName]
           -> LHsType GhcPs     -- Always a HsForAllTy
           -> (ConDecl GhcPs, [AddAnn])
mkGadtDecl names ty
  = (ConDeclGADT { con_g_ext  = noExtField
                 , con_names  = names
                 , con_forall = L l $ isLHsForAllTy ty'
                 , con_qvars  = mkHsQTvs tvs
                 , con_mb_cxt = mcxt
                 , con_args   = args
                 , con_res_ty = res_ty
                 , con_doc    = Nothing }
    , anns1 ++ anns2)
  where
    (ty'@(L l _),anns1) = peel_parens ty []
    (tvs, rho) = splitLHsForAllTyInvis ty'
    (mcxt, tau, anns2) = split_rho rho []

    split_rho (L _ (HsQualTy { hst_ctxt = cxt, hst_body = tau })) ann
      = (Just cxt, tau, ann)
    split_rho (L l (HsParTy _ ty)) ann
      = split_rho ty (ann++mkParensApiAnn l)
    split_rho tau                  ann
      = (Nothing, tau, ann)

    (args, res_ty) = split_tau tau

    -- See Note [GADT abstract syntax] in GHC.Hs.Decls
    split_tau (L _ (HsFunTy _ (L loc (HsRecTy _ rf)) res_ty))
      = (RecCon (L loc rf), res_ty)
    split_tau tau
      = (PrefixCon [], tau)

    peel_parens (L l (HsParTy _ ty)) ann = peel_parens ty
                                                       (ann++mkParensApiAnn l)
    peel_parens ty                   ann = (ty, ann)


setRdrNameSpace :: RdrName -> NameSpace -> RdrName
-- ^ This rather gruesome function is used mainly by the parser.
-- When parsing:
--
-- > data T a = T | T1 Int
--
-- we parse the data constructors as /types/ because of parser ambiguities,
-- so then we need to change the /type constr/ to a /data constr/
--
-- The exact-name case /can/ occur when parsing:
--
-- > data [] a = [] | a : [a]
--
-- For the exact-name case we return an original name.
setRdrNameSpace (Unqual occ) ns = Unqual (setOccNameSpace ns occ)
setRdrNameSpace (Qual m occ) ns = Qual m (setOccNameSpace ns occ)
setRdrNameSpace (Orig m occ) ns = Orig m (setOccNameSpace ns occ)
setRdrNameSpace (Exact n)    ns
  | Just thing <- wiredInNameTyThing_maybe n
  = setWiredInNameSpace thing ns
    -- Preserve Exact Names for wired-in things,
    -- notably tuples and lists

  | isExternalName n
  = Orig (nameModule n) occ

  | otherwise   -- This can happen when quoting and then
                -- splicing a fixity declaration for a type
  = Exact (mkSystemNameAt (nameUnique n) occ (nameSrcSpan n))
  where
    occ = setOccNameSpace ns (nameOccName n)

setWiredInNameSpace :: TyThing -> NameSpace -> RdrName
setWiredInNameSpace (ATyCon tc) ns
  | isDataConNameSpace ns
  = ty_con_data_con tc
  | isTcClsNameSpace ns
  = Exact (getName tc)      -- No-op

setWiredInNameSpace (AConLike (RealDataCon dc)) ns
  | isTcClsNameSpace ns
  = data_con_ty_con dc
  | isDataConNameSpace ns
  = Exact (getName dc)      -- No-op

setWiredInNameSpace thing ns
  = pprPanic "setWiredinNameSpace" (pprNameSpace ns <+> ppr thing)

ty_con_data_con :: TyCon -> RdrName
ty_con_data_con tc
  | isTupleTyCon tc
  , Just dc <- tyConSingleDataCon_maybe tc
  = Exact (getName dc)

  | tc `hasKey` listTyConKey
  = Exact nilDataConName

  | otherwise  -- See Note [setRdrNameSpace for wired-in names]
  = Unqual (setOccNameSpace srcDataName (getOccName tc))

data_con_ty_con :: DataCon -> RdrName
data_con_ty_con dc
  | let tc = dataConTyCon dc
  , isTupleTyCon tc
  = Exact (getName tc)

  | dc `hasKey` nilDataConKey
  = Exact listTyConName

  | otherwise  -- See Note [setRdrNameSpace for wired-in names]
  = Unqual (setOccNameSpace tcClsName (getOccName dc))

-- | Replaces constraint tuple names with corresponding boxed ones.
filterCTuple :: RdrName -> RdrName
filterCTuple (Exact n)
  | Just arity <- cTupleTyConNameArity_maybe n
  = Exact $ tupleTyConName BoxedTuple arity
filterCTuple rdr = rdr


{- Note [setRdrNameSpace for wired-in names]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In GHC.Types, which declares (:), we have
  infixr 5 :
The ambiguity about which ":" is meant is resolved by parsing it as a
data constructor, but then using dataTcOccs to try the type constructor too;
and that in turn calls setRdrNameSpace to change the name-space of ":" to
tcClsName.  There isn't a corresponding ":" type constructor, but it's painful
to make setRdrNameSpace partial, so we just make an Unqual name instead. It
really doesn't matter!
-}

eitherToP :: Either (SrcSpan, SDoc) a -> P a
-- Adapts the Either monad to the P monad
eitherToP (Left (loc, doc)) = addFatalError loc doc
eitherToP (Right thing)     = return thing

checkTyVars :: SDoc -> SDoc -> Located RdrName -> [LHsTypeArg GhcPs]
            -> P ( LHsQTyVars GhcPs  -- the synthesized type variables
                 , [AddAnn] )        -- action which adds annotations
-- ^ Check whether the given list of type parameters are all type variables
-- (possibly with a kind signature).
checkTyVars pp_what equals_or_where tc tparms